Improvement in prisms



A. K. EATON.

Prism.

N0,|60,756 patentedmarcmmaw.

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UNITED STATES PATENT OFFICE.

ASAHEL K. EATON, OF BROOKLYN, NEW YORK.

IMPROVEMENT iN PRISMS.

Specification forming part of Letters Patent No. 160,756, dated March i6, 1875; application filed August 4, 1874.

To all whom it may concern:

Be it known that I, AsAEEL K. EATON, of Brooklyn, State oi' NeaT York, have invented a Direct Brism, of which the following is a specication:

My invention consists in the construction of a prism, either hollow and iilled with bisulphide of carbon or other dispersive iluid, or solid, oi' glass or other transparent substance, in such a manner that the incident ray and the mean ray of the emergent pencil shall be in the same right line-i. o., the action of the prism is direct, giving obvious advantages over the common i'orm.

I will coniine my description to the hollow bisnlphide-of carbon prism, since the same principle of construction applies to all.

It consists, as I usually construct it, of a prismatic frame-work, of iron, brass, or other material, having nearly the following angles: sixty degrees, thirty degrees, and ninety degrees. 'Ihe angles, except that ot' sixty degrees, may be varied considerably. Upon the side a b of the prismatic frame a b c I cement a piece oi' thick crownglass, the edge ot' which is represented by A B a b. 'Ihe end oi' this plate a A is cut and polished at right angles, or nearly so', to the side of the plate. Upon the end b c ot' the prismatic frame I cement a piece ot' thin plate-glass. The other side ofthe prism (represented by a o) is of metal, and a part of the frame.

rIhe prism thus constructed, having been iilled with bisulphide of carbon or otherwise, is ready for use. rIhe incident ray from the slit telescope of a spectroscope, or any other source, striking the polished end of the thick plate A B a b, is retracted to d, at which point, passing into the bisulphide ot' carbon, it is retracted again, reaching the end ofthe prism at o, where, as it passes into the air, it is again retracted, assuming a direction, c yr, exactly coincident with the incident ray I K.

Dispersion, or" course, accompanies these several reiiactions; but I have described the course of the niean ray only.

The surface A B of the plate is not used, and therefore is ground rough, or covered, so as to exclude light.

The prism may be used, obviously, with either end toward the source of light; but more than three times the dispersion is produced when the incident ray is received upon the broad end of the prism b c than when used in the reverse position.

The advantages arising from this form of prism are as follows:

First, its direct action is a most obvious advantage in all its applications to spectroscopic or other investigations.

Second, when the incident ray is received upon the narrow end of the prism from the slit telescope ot' a spectroscope it gives fully the dispersion ot' an ordinary sixty degrees b1- snlphide-oicarbon prism, and even with a very wide slit gives great uniformity and sharpness of delinition.

rIhird, it' the incident ray strikes the end of the plate in the direction I K the Fraunhofer lines are easily seen by the naked eye by means of the prism alone, no slit or collimator being used, the light being taken from a window or from some large aperture. Ihe bright band of colored `dames is also readily seen by the prism alone. In this case the prism does not a-ct quite directly.

Fourth, by receiving the light from the slit telescope upon the broad end of the prism, the dispersion is so greatly increased that the solai' lines Dl and DZ may be so widely separated that the nickel line is readily seen between them. This use ol' the prism requires careful adjustment.

The same general results, varying in degree, are obtained by the use of solid dispersive mediums, such as dint-glass, &c., the plate ot' crown-glass being cemented upon the side oi the iiint prism. The angles will, ot' course, vary with any considerable variation otl the index ot' refraction.

I claim as my invention- A prism having upon one of its sides a piece ot'crown-glass, having one or more polished ends, substantially as herein set forth.

ASAIIEL K. EATON,

YVitnesses:

W. E. OsEoEN, A. IL OsBoRN. 

